It is known there are three elements in the structure of a pressure cooker (steam pressure cooker): (1) High steam pressure resistant; (2) opening of cover is easy and there is a good air tightness and (3) appropriate pressure valve with a safety valve. When food to be cooked is placed in a pressure cooker and the cooker is heated up to an appropriate steam pressure, the rising of steam temperature raises the temperature of the food itself and thus, a lot of cooking time can be saved. Therefore, a pressure cooker should be high pressure resistant and thermal resistant. So, it should have a special structure and the question is, a pressure cooker should have a relatively large and heavy structure, and its application is difficult, and so on.
General house using pressure cooker has the following coupling arrangements Thread Coupling (as shown in FIG. 1 A); Latch Coupling (FIG. 1 B) and Oval Cover Coupling (FIG. 1 C). Both of them have the following common disadvantages: (1) Since a pressure cooker requires high pressure resistance with good air tightness, the complicated coupling makes application difficult and because of the limit in material and shape of cooker, production precess is difficult and the cost is high. (2) Such a pressure cooker uses air holes for pressure release, negligence in operation will clog the air hole and then, there is an extra high pressure in the cooker and there is even a risk of explosion. With such riskful disadvantages, even though pressure cookers are good kitchen utensils, consumers are hesitate to buy them and therefore, its popularity is affected.